Yahoo said it uncovered another cyberattack in which data from more than one billion user accounts was compromised in August 2013, according to Reuters.
The number of users affected by the attack is almost double the number of users impacted by a data breach in September 2014, according to the article.
Yahoo officials said they discovered the breach after reviewing data provided to them by law enforcement. While officials have not yet uncovered the cause of the August 2013 breach, they said payment card data and bank account information for the company was not stored on the affected system. Information stolen in the August 2013 breach "may have included" names, email addresses, telephone numbers, dates of birth, hashed passwords and, in some cases, encrypted or unencrypted security questions and answers.
Officials said they believe the 2013 and 2014 breaches are "likely" unconnected.
After learning of the breach, Yahoo required all of its customers to reset their passwords.
Yahoo officials claim the hackers involved in the September 2014 breach were working on behalf of a government. The hackers reportedly accessed the company's proprietary code and learned to forge cookies, which enabled them to access accounts without imputing a password, according to the article.
Verizon Communications, which currently has an agreement in place to purchase Yahoo for $4.83 billion, said in a statement that it will "review the impact of the new development before reaching any final conclusions" on the potential acquisition. A Yahoo spokesperson said the company has been in communication with Verizon since discovering the breach and that the company is "confident the incident will not affect the pending acquisition," according to the article.